In the context of the present invention, it is to be taken that the term “fluid” applies to any material that displays liquid-like or gas-like behaviour or physical properties.
The treatment of fluids by disinfection, for example, is an important process enabling the safe and efficient use and/or consumption of these fluids in industrial and domestic environments. For example, the ability to disinfect water for general consumption by animals and/or humans including drinking and recreational use is paramount. An example application of such treated water includes production liquid for the preservation of fresh cut flowers. When treating fluids it is also critical that the flow of the given fluid is determined and/or controlled.
Prior art techniques used for disinfecting fluids, such as for example in Australian Patent 53032/98 (735166), Australian Patent 11859/97 (702918) and Australian Patent 24394/95 (685630), make use of the ability of silver ions to effectively destroy micro-organisms such as bacteria and viruses. However, in these prior art systems, the silver that is being introduced into a given fluid requires sophisticated electronic equipment for either monitoring the amount or dose of silver being introduced or monitoring the volumetric flow of fluid to be treated. Moreover, regulatory authorities throughout the world now stipulate their own varying individual maximum levels of silver that may be added to fluids for their treatment. These various regulations make it difficult and expensive to control the amount of silver to be released into a given flow of fluid.
Other prior art systems, such as disclosed in DE 4107708, attempt to accurately monitor fluid flow. These systems require the use of delicate on/off flow switches and are therefore, expensive. Generally, the flow switches of prior art systems are made using glass encased reed switches and magnets of differing types. Reed switches, in particular, are easily cracked and as a result may fail to perform. Furthermore, the circuits required to control these systems often fail especially where corrosion occurs as would be expected when placed in close proximity or contact with the various fluids being treated, in the event of these failures, the prior art systems cannot provide for regulated introduction of sliver into a fluid.
Prior art silver disinfection systems may also have a tendency to cause an overdose of silver into the fluid. Notwithstanding the toxic effects of excessive silver consumption, a further problem associated with silver overdosing has been shown, namely, de-oxygenation. When excessive amounts of silver are introduced into a body of fluid the excess silver will absorb the available free oxygen and may use the absorbed oxygen to destroy anaerobic micro-organisms by the process of oxidation leaving the fluid in a de-oxygenated form. The de-oxygenated fluid then becomes an environment that is conducive to the multiplication and resultant re-infection of micro-organisms. This re-infection is also assisted by the fact that dissolved silver in a relatively short time, plate out to the walls containing the fluid or, being heavy will fall out of suspension removing the active silver from the fluid. Thus, there is a need to maintain a correct balance of silver concentration for successful disinfection.
Prior art systems such as that disclosed in Australian Patent 53032198 (735160) have provided a solution to the problem of plating by producing suspended silver particles instead of silver ions. Such particles are not soluble and cannot plate out and, in turn, as the particles are of pure silver and not silver ions forming silver salts, they may not produce toxic effects in high doses. However, complex circuits are required to produce pure silver particles and this is a disadvantage, particularly when a readily useful and easily accessible means of disinfection is required in the market. Furthermore, the lack of plating displayed by silver particles is a disadvantage when it is desirable to treat the surface or walls of a fluid carrier to produce, for example, a bacteriostatic coating of silver preventing biofilm build up.
It is therefore an object of the present invention to provide a method and apparatus, which ameliorates at least one disadvantage of the prior art arrangements. It is also an object of the present invention to provide a method and apparatus providing for the control or monitoring of the introduction of chemically active forms of metal into a fluid that may flow at a variable rate. It is also an object of the present invention to provide a method and apparatus for providing control over the plating out effect of an introduced metal on the walls of a fluid carrier.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art on or before the priority date of the claims herein.